Aquaculture nets or fish-farming nets are used to raise aquatic life such as fish. The aquaculture net keeps the aquatic life controlled and contained and protects the aquatic life inside the net against predators such as sharks, piranhas, nutrias, seals and sea lions.
The aquaculture nets are usually of the chain link fence type. This is a fence of steel wires woven into a diamond pattern. The meshes have a dimension that is smaller than the dimension of the fish contained in the nets. Each steel wire is pre-formed by bending so that it exhibits a wavy pattern with maxima and minima. The maxima of a steel wire interlock with the minima of a neighboring wire to form the patterns of a series of diamonds.
Aquaculture nets of the chain link fence type have proven to be successful to control the aquatic life and to protect against predators.
The dimensions of such an aquaculture net are considerable. An example of a typical dimension is 30 m×30 m×15 m (square) or 50 m×15 m (round), the last dimension being the depth of the net inside the water and the first two dimensions being the width and length of the net at the water surface. As a matter of example, a net made of galvanized steel wire, or a copper nickel cladded wire, and of the above-mentioned dimensions has a weight above 4 metric Tonnes.
Net bottoms only are usually heavier than 1000 kg. With these high net weights, the bottom has become an important issue since it changes shape under the weight. A flat bottom sinks and gets bent downwards (FIG. 1a). As a result, the walls are also pulled downwards and the net shape is not optimal anymore with a great loss of useful volume. Additionally, the lowest points of the bottom will be at depths greater than 20 meters below sea or ocean level. At these great depths, diving is no longer allowed and divers can no longer reach the bottom of the net. So for divers to reach the bottom of the aquaculture nets, these nets need to be less deep, resulting again in less net volume. This is a great disadvantage.
JP52-122597A discloses a metal net with a hexagonal bottom, wherein the hexagonal bottom thereof is composed of six equilateral triangle. US2010/0319625A1 discloses an aquaculture net with a regular octagonal bottom. The bottom thereof can be formed by a single piece of steel wire mesh. Alternatively, the bottom is formed by either eight parts in the form of equilateral triangles or by four parts in the form of equilateral triangles and by a cross of five square parts. Although the bottom of the aquaculture nets in these publications comprises several parts, the sag of bottom is not addressed and it is still a problem.
To solve this problem ropes are attached to several points of the bottom net and tied to a floatable structure or buoys that prevent the bottom from deforming (FIG. 1b). However, this results in a bottom net with smaller and multiple sags as deepest points. So the dead fish are collected in various sags rather than in one point or according to one single line. This generates extra work for the divers cleaning up the dead fish and makes it difficult to use with automatic dead fish extractors.
Since divers are no longer an option with big dimension aquaculture nets, other solutions are needed.